The prior art is well documented with examples of positive displacement flow devices. One example of this is described in U.S. Pat. No. 6,666,666, to Gilbert et al., which teaches a pump including multiple, axially stacked positive displacement fluid device sections, such as circumferential piston pumps having chambers and contra-rotating chambers. As indicated, the device can be similarly employed as a fluid motor.
The stacked sections are arranged within an outer retaining barrel in one or more stages. The pump is particularly suitable for installation downhole in the casing of a wellbore. As further described, each section includes a pair of rotors fit to shafts which are rotatably supported on hard faced bearings between the shafts and the bosses. Each pump section draws fluid from an inlet port and discharges fluid to a common and contiguous discharge manifold. The inlets of the pump sections for a suction stage communicate with a fluid source. Cross-over sections route fluid between stages. Successive pressure stages draw fluid from the cross-over fit to the preceding stage's discharge manifold.
Other references of note include the power plant for self-propelled vehicles of Capdevielle, U.S. Pat. No. 3,828,555, which two pipelines are inserted between a high-pressure tank and a low-pressure tank containing a hydraulic fluid. A hydraulic motor is inserted in the first pipe line and is adapted to actuate the driving shaft of the vehicle through a freewheel coupling. A motor-pump unit is inserted in the other pipe line. This motor-pump unit has a relatively low-rated power output and is continuously operating at the same speed, such that the design is described as being particularly suited to automotive applications intended for service requiring frequent stops.
WO 2009/124461, to Xiang, teaches a hydraulic power engine and generator group apparatus including each of a first part in the form of an energy conversion magnifying power region, a second part speed adjustable direct current motor connected in series with accumulators, a third part reduction gear box and a fourth part hydraulic system with hydraulic cylinders.
Pette, US 2014/0141933, teaches a drive system and method including a gearbox system, a first hydraulic motor driving a first input shaft, a second hydraulic motor driving a second input shaft, a drive pump driving the first and second hydraulic motors, and a system control for controlling the drive pump, the clutch assembly, and the first and second hydraulic motors. The gearbox system includes the first input shaft having a first input gear driving a first output gear on an output shaft, the second input shaft having a second input gear driving a second output gear disengageable from the output shaft, and a clutch assembly for engaging the second output gear with the output shaft. The clutch assembly includes a clutch to engage the second output gear with the output shaft, and a fluid access channel through a rotary manifold to provide pressurized fluid to activate the clutch.